# vco high tuning at 100 MHz

Discussion in 'Homework Help' started by oozy, Dec 24, 2013.

1. ### oozy Thread Starter New Member

May 7, 2013
2
0
dear all,,
am really stucked with this assignment and really appreciate whoever can help me with the calculations.
We were asked to design a high tuning vco at the frequency of 100 Mhz.
with some help i've managed to design this circuit shown in the image, but still didnt understand the way of calculations and how to obtain the value for each of the resistors and capacitors.

Eventhough if any one can help with another design, i'll be so happy aas it'll help me to overcome this course
thanks

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2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,070
If you designed that, I'll eat my hat.

If you designed it, you should know the answers to these questions:

What purpose does R4 serve?
What purpose does C3 serve?

3. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
it looks like c3 is to block the tuning voltage off the base of the transistor. r4 to limit the current of the circuit.

Apr 5, 2008
16,974
2,962
Hello,

It is clear that you made a mistake in copying the circuit:
(Thanks MikeML).

The control voltage is on the wrong side of the L1 coil in "your" schematic.
That way there is a wrong isolation between the tuning circuit and the tuning voltage.

Bertus

Last edited: Dec 25, 2013
5. ### oozy Thread Starter New Member

May 7, 2013
2
0

thanks for ur rudness
am a computer specialized and have no good abilities with electronic stuff
i thought some one here is goin to help with pleasure not jst making fun of ppl
dont ever think if ur better than sum one in a single thing u can be superior.

yes i copied the circuit and did that modification by purpose mister!, the results are very accurate and an expert have just approved to me
you nerds:
i guess its better to celebrate ur christmas rather than making fun of ppl in an academic forum!!

6. ### MrChips Moderator

Oct 2, 2009
14,282
4,195
Holy crap! Some guy copies a circuit as his own design and wants us to explain how to calculate the values.

Then he gets upset and calls us rude because we point out mistakes in his copy.

7. ### WBahn Moderator

Mar 31, 2012
20,064
5,665
I do to.

Unfortunately, this is indicative of an increasingly common attitute of entitlement.

Apr 5, 2008
16,974
2,962
Hello,

I will take the part numbering of the original circuit.
C3 and C6 are 100 nF and NOT 104 pF as in your schematic.
C6 is to decouple the powersupply.
C3 is there to provide an RF ground for the transistor.
The 10 Ohms resistor R4 is to isolate the RF circuit from the powersupply and limit the current.
C5 is 3.3 nF to 4.7 nF and NOT 332 pF.
C3 will provide ground to the tuning circuit and decouple the tuning voltage.
L1 is the coil that determines the tuning frequency with C1, C4 C7 and D2.

Bertus

oozy likes this.